It is well-known that the formation of a cured coating comprising a thermosetting organopolysiloxane composition on the surface of a substrate, such as ordinary paper, coated paper, plastic films, etc., facilitates the release of the substrate from a tacky material, and enables the prevention of the adhesion between substrates. The known organopolysiloxane compositions usable therein, are of two general types from the viewpoint of curing reaction mechanism, i.e., those undergoing addition reaction and those undergoing condensation reaction. Most of the hitherto known releasing compositions can be applied suitably to such uses as to achieve their purpose even when they have rather low bond release strength e.g., as a coating for pressure-sensitive adhesive labels and tapes, furniture paper, decalcomania and so on.
However, in the field where high bond release strength is required, for instance, process paper for synthetic resins with tackiness, asphalt wrapping paper, double-sided tape, for which tight releasability is required in order to impart differential releasability to either side, stretched polypropylene tape for which somewhat tight release is required, or so on, application of hitherto known releasing compositions has been regarded as almost hopeless because of severe restrictions imposed on their uses.
With the objective of solving the problem as described above, a condensation reaction type organopolysiloxane composition to which a siloxane-soluble resinous substance (MQ resin constituted by R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units) is added (Japanese Patent Kokai 8527/'74; the term "Japanese Patent Kokai" as used herein means an "unexamined published Japanese Patent application"), a condensation reaction type organopolysiloxane composition which comprises silicone modified with alkyd, melamine or like resin (Japanese Patent Kokoku 13507/'86; the term "Japanese Patent Kokoku" as used herein means an "examined Japanese patent publication"), and so on have been proposed. However, those compositions have the defects that they are inferior in curability, and the obtained coats are also inferior in residual adhesion and blocking resistance.
As the addition reaction type organopolysiloxane compositions, there have been proposed those blended with toluene-soluble copolymers constituted by R.sup.1.sub.3 SiO.sub.1/2 units (Japanese Patent Kokai Nos. 139452/'80 and 155257/'81), those blended with toluene-soluble copolymers constituted by R.sup.1.sub.3 SiO.sub.1/2 units, SiO.sub.2 units, and R.sup.1.sub.2 SiO or R.sup.1 SiO.sub.3/2 units (Japanese Patent Kokoku 5418/'82), those blended with silica powder (Japanese Patent Kokoku 11628/'84), and so on. However, such additives had to be used in a considerably large amount in order to fully achieve their effect in controlling the resulting compositions so as to acquire from medial to tight release, and their compatibility with bases, e.g., vinylsiloxane, hydrogensiloxane, etc. y, was not high enough for the purpose. Therefore, such additives suffered from a disadvantage that they retarded curing speed to a great extent. In addition, since the coats thus obtained lowered the tackiness of the pressure sensitive tackifier, and changed greatly the stability of adhesion power upon storage, it was hard to stably maintain the initially controlled release strengths.
Moreover, the above-cited copolymers are, in general, a viscous liquid or solid, so it is hard to use them in quantity unless a solvent is used. Consequently, they were used in the form of a solution. However, such solutions were difficult to handle because their viscosities changed susceptibly with dilution ratio and temperature and, what was worse, they tended to cause "a cissing phenomenon", i.e., produce non-continuous coatings, when coated on substrates because of their relatively low molecular weights. Therefore, organopolysiloxane compositions containing them had the defect of being hard to coat uniformly onto a substrate.